Process for treating hydrocarbons



April 6, 1943.

w. A. scHULzE er1-Al. 2,315,875 PROCESS FOR TREATING HYDROCARBONS Filed001'.. 28, 1941 l 23' /IQA NWf'l-IOD QNIZINVLNBdBCI IJJ [EEZ D I ..1Ou-'O mm D@ INVENTORS CD WALTER A. SCHULZE LLOYD C. MORRIS Patented Apr.6, 1h43v i maar UNITED STATES PATENT GFICE PROCESSFOR TREATNGHYDROCARBONS Walter A. Schulze and Lloyd C. Morris, Bartlesville, Okla.,assignors to Phillips Petroleum Company, a corporation o! DelawareApplication October 28, 1941, Serial No.` 416,882

19 Claims.

The importance of sulfur removal from gasoline: -and special motor fuelsof all types has been emphasized by the increasingly higher anti-knockspecifications and the practically universal use of anti-detonantadditives such as tetraethyl lead. It has been established that theoctane number improvement obtained by addition of lead alkylanti-detonants to motor fuels is dependent on the total amount and kindof sulfur compounds in octane number and the sulfur content of the othercomponents. Thus the sulfur content of the blending stocks is of majorimportance, and justiles the use of extensive desulfurization treat-=ment.

Various chemical treating processes-have been proposed for reducing thesulfur content of hydrocarbon oils and some of these have specificapplication to certain refining operations for ordinary motor fuels. lsocatalytic processes have been proposed which accomplish desulfurizationby more or less severe treatment of hydrocarbon oils at elevatedtemperatures. These prior processes often are justified in that thesavings obtained are greater than the cost of equipment, product losses,and operation. However, in many cases a more efiicient and inexpensivemethod of desulfurization is desirable.

said fuels, and that tremendous savings result from the reduction of thesulfur content of hydrocarbon oils used in the production of said fuels.

The benefits derived from desulfurization may be measured in terms ofdecreased amounts of tetraethyl lead required to -produce a given octanerating. In other applications, the benefits may be measured in increasedvolumes of fuels produced according to specifications limiting theconcentration of anti-detonant compound. In either instance, themanufacture and/or 'segregation of hydrocarbon oils of low sulfurcontent and high octane rating have become related problems to thereilner.

The trend toward higher octane ratings and the manufacture of specialfuels have led to processes involving synthesis of certain hydrocarbonssuch as isooctane and the like, and to rather elaborate procedures forthe segregation of the more desirable hydrocarbons occurring in complexmixtures such as crude oil and natural gasoline. For exe ample, in themanufacture of 100 octane fuels containing a maximum of 3 ml. per gallonof tetraethyl lead uid, commercial isooctane is ordinarily onecomponent. Other hydrocarbons, such as isopentane, are blended with theisooctane to furnish the desired volatility, and special naphthafractions are generally added to' increase the volume of the blend tothe limit conforming to the specifications on octane number and tetraethyl lead concentration. In such operations, the total volume of fuelwhich can be prepared from a unit volume of isooctane will depend uponthe We have now discovered a process whereby the desulfurization ofhydrocarbon oils valuable as high octane number blending stocks can becaused to coincide with the operations which produce and/or segregatesaid stock from complex hydrocarbon mixtures. By our method ofoperation, the major part of the desulfurization occurs in theparticular mode of separation of high octane stocks from low octanestocks so that said high octane stocks may not require furtherdesulfurization treatment. However, our process provides for additionalsulfur reduction if lt is desirable.

Our invention is to a large extent based on a novel interpretation ofthe boiling point, volatility and partial pressure relationshipsexhibited by the sulfur compounds in hydrocarbon mixtures and extendsconventional treating and fractionation methods to accomplishdesulfurization.

The principal object of the present invention is to provide an improvedprocess of preparing an isopentane blending stock. Another object is toprovide an improved process of freeing isopentane from sulfur at thesame time as or in conjunction with its'preparation. Another object isto pro-- vide a process for simultaneously preparing low sulfur-contentisopentane blending stock and low sulfur-content pentane-free gasoline.Still another object is to providean improved process ofdcsulfurization. Another object is to provide an improved process ofpreparing blending stocks high in iso-paraflins above Cs andsimultaneously a blending stock high in isop'entane and obtaining as aJoy-product a blending` stock high .in npentane. Numerous other objectswill more fully hereinafter appear.

This invention may be understood from the following description taken inconjunction with the sweetened pentanes are then fractionated to form anoverhead product consisting essentially of isopentane in whichunexpectedly the methyl sulfide appears (in view of its boiling pointthis compound would not be expected to appear in the isopentane but toremain in the bottom d product) and a bottom product comprising npentaneand the high boiling disulildes. The isopentane fraction thus obtainedmay then be dehydrated and subjected to the action of anhydrous cupricchloride to remove the methyl sulfide therefrom and give a blendingstock consisting essentially of isopentane and generally containing lessthan 0.0001% of sulfur. The isopentane fraction prior to treatment forremoval of methyl suliide usually contains less than 0.01% of sulfur andfor many purposes this low sulfur content, which is mainly attributableto the presence of methyl sulde, is not objectionable in which case thestep of removal of the methyl sulto form one or more fractionscomprising hydrocarbons of C. to C including iso-hexanes andiso-heptanes, for example either a single fraction of pentane-freegasoline or a plurality of fractions comprising an iso-hexane fractionand an iso-heptane fraction, and perhaps even an isooctane fraction.This fraction or fractions comprising oneor more iso-para'mns may betreated as before for removal of albi sulfides, if desirable. The bottomproductfrom this fractionation may comprise the n-hexane, n-heptane andheavier hydrocarbons and thel very high boiling sulfur compoundsparticularly the disulfldes' formed in the sweetening step.

My process takes advantage of the discovery that the distribution ofthe'mercaptans in the first fractionation departs from the expected oneand involves the appearance of va larger-thanexpected percentage of themercaptans in the light overhead pentane fraction and of asmallerthan-expected percentage in the'heavy bottom.

" In addition, the separation of hydrocarbons at a given boiling pointinvolves simultaneous separation'of mercaptans at a materially higherboiling point. Thus sulfur compounds boiling materially above 97 F. (theboiling point of n-pentane); even as high as 155 F., come .over with thepentanes.

This departure from expected behavior in the separation of the pentanefraction is taken advantage of, in accordance with my invention, bysubjecting the pentanes to a sweetening step to convert the mercaptanstherein to disulfldes thereby producing such a great difference inboilasians ing point between the disulfides formed and the isopentanethat fractionation of the sweetened pentanes effects production ofisopentane free from disulfldes. However the methyl sulfide unexpectedlyappears largely in the isopentane fraction so produced and, if excessivein amount, is preferably removed by treatment of the anhydrousisopentane with anhydrous cupric chloride. The unexpected distributionof the mercaptans and other sulfur compounds, referred to above, resultsin a lower concentration and a higher average boiling point ofmercaptans in particular, in the bottom product from the rstfractionation. Upon sweetening this bottom product such relatively highboiling mercaptans as are present are converted to disuliides of veryhigh boiling point. Upon fractionation of this sweetened bottom productthese very high-boiling sulfur compounds are very readily separated fromthe gasoline and appear in the heavy bottoms. Also, in view of the lowconcentration of these disuldes in the sweetened bottoms, theirdistribution in accordance with known distribution laws causes them tobe absent from the light overhead gasoline product in detectableamounts. However the higher-boiling alkyl suldes may go overhead andappear in the pentane-free lighter fraction or fractions inobjectionable amounts, although usually lthe amount of alkylsulfldes inthe overhead product'to 10 %-bottoms will be less than 0.015%. Treatmentof this overhead product with anhydrous cupric chloride reduces thesulfur content to not over 0.010%. Whether the overhead product isrecovered as such or in the form of individual fractions of isohexanes,isoheptanes and n-hexane, or of the isohexanes and isoheptanes inadmixture with the n-hexane recovered separately, it is preferred thatsuch isoparaiiinic stocks have a sulfur content of less than 0.010%. Asbrought out below, if the components are separately recovered and thenblended, a lower sulfur content is possible than where they arerecovered together.

, As stated previously. special high octane fuels are often prepared byblending synthetic isooctane with other stocks chosen for high octanenumber and proper boiling range and often segregated in relatively pureform. Our invention will be described in terms of such an operation,although the basic principles are of wide scope and general application.For our process, any low-boiling liquid hydrocarbon mixture preferablyin the gasoline range, such as straight run, .naturaL polymer, or vaporrecovery gasoline, may be the starting material. However, we ordinarilyprefer a natural or straight run gasoline containing maximum amounts ofisoparafns and minimum amounts of oleiins and cyclic hydrocarbons whichcomplicate the desired separations.

` A hydrocarbon mixture of the described nature is the gasolineseparated by conventional methods from natural gas and termed naturalgasoline. For our purposes, the natural gasoline should be substantiallyfree of butane and lower boilingI hydrocarbons and have a boiling rangeof from about '10 to about 300 F. Often the retention of slight amountsof absorption oil will up to some predetermined v n-ButylI1Jeircapti1ii- This mixture may comprise varying amounts of some or allof the following hydrocarbons listed below with their approximateboiling points and tane numbers.

A. S. T. M. octane Boiling int a @tt number Hydrocarbon 21 300 andhigher.

Octanes and nonanes 211 to- The higher Pboiling hydrocarbons of 8 ormore carbon atoms are not ordinarily considered for careful segregationof a single component because of the increasing complexity of themixture and the higher boiling points, although in some cases it may bedesirable to extend the .process of separation to include isoparamns ofhigh octane number in this or higher boiling ranges. It will be seenfrom the above table that the least desirable components of the mixturefrom the standpoint of octane number are the normal paramns. Thus,isopentane is the most desirable component to furnish high octanenumberand volatility in a blend, while normal vpentane is less desirable.Similarly the isohexanes and isoheptanes are particularly desirable forthe special naphtha blending stocks, and n-heptane is the leastdesirable constituent. In view of these considerations, a preferredprocedure is to segregate the isopentane s and the fractions comprisingisohexanes and isoheptanes maximum boiling point. 'I'he n-pentane,n-hexane, n-heptane and the high-boiling ends of the gasoline, which arethus excluded, may then be further processed or used for other purposeswherein the low-octane number or unsatisfactory boiling range are notundesirable.

The same natural gasoline described above would ordinarily be free ofhydrogen sulfide following removal of butane, the hydrogen sulde beingremoved prior to, at the same time as, or after the butane. Some methylmercaptan would also be removed in the butane separation. 'I'heremaining sulfur compounds would include the following:

(10o mms' Methyl mercaptam-, Ethyl mei-captan. Methyl sulfide...i-Propyl merptsn. t-Butyl mei-captan... nPropyl mercaptan Isobutylmex-captan. Ethyl sulde When the sour stock is sweetened by conven- Ktional sweetening procedures the lower-boiling mercaptans are convertedto the corresponding disuldes having the following boiling points:

Boilingr point F. l (760 mm.)

Compound ation Thus, higher-boiling mercaptans are converted todisulfides having still higher boiling points beyond the designatedboiling range of the gasoline and hence concentratable in the highestboiling fraction.

In accordance with our invention the sour hydrocarbon mixture isfractionated prior to sweetening in an operation which produces anoverhead fraction consisting of Cs' hydrocarbons and a bottoms fractioncomprising substantially pentane-free material. A sharp separation isessential to remove substantially all of the n-pentane from the bottomsfraction.

f In this fractionation of the sour gasoline, methyl and ethylmercaptans are substantially removed from the hexanes and heavierfraction and taken overhead with the mixed pentanes, whereas if thebutane-free gasoline is sweetened prior to the depentaniz'ing step, thedimethyl and diethyl disulfides formed remain to a large extent in thehexane and heptane fractions.

purity is obtainable if desired. The n-pentane g which contains themajor portion of the sulfur compounds distributed in the C's fraction bythe initial fractionation, may be employed for blending with loweroctane fuels. It will usually be desirable to fractionate the n-pentanein order to obtain as the overhead product n-pentane essentially freefrom sulfur and as the bottom product containing the relativelyhigh-boiling sulfur compounds.

The valuable isopentane concentrate following the described operationordinarily has a low sulfur content, containing substantially onlymethyl sulfide. This impurity may then be removed by means of anhydrouscupric halide reagents as described in our copending application, SerialNumber 318,648, of which this application is a continuation-impart, andisopentane substantially sulfur free is thereby produced. The method ofthat application comprises contacting the sweetened hydrocarbon oil insubstantially anhydrous form with a reagent comprising substantiallyanhydrous cupric chloride to remove the alkyl suldes from the sweetenedoil.

The substantially pentane-free mixture from thegoriginal fractionationis then sweetened in a separate unit and the sweetened mixture isfractionated to remove heavy ends and/or to segregate the high-octaneiso-paraillns. The extent and the sequence of the fractionationoperations may vary with the volume and quality of the special naphthacuts desired. ConventionalV procedures may be employed to obtain theisohexanes and isoheptanes together or as separate fractions, usuallywith a maximum boiling point of about 210 F. When the isohexanes andisoheptanes are recovered as separate fractions, n-hexane is removed byan intermediate fractionstep. The isoparain stocks thus obtained willhave a greatly reduced sulfur'content compared to the total pentane-freegasoline orto heavier hydrocarbons since the maior portion of the sulfurimpurities is concentrated in' the \highest boiling hydrocarbonfraction'. When the combined or separate overhead fractions have an endpoint below around i90-200 F., the sulfur compounds comprise mainlyethyl sulnde. Thus, a treatment with our reagent for the removal ofalkyl sulfides will effect a significant further reductionl in thesulfur content.- Also, when the isoparaflins` are not segregated and thepentane-free gasoline "is merely subjected to a de-oilingfractionationfr the removal of high-boiling ends, the sulfur ontent ofthe de-oiled gasoline may be reduced to a satisfactory low figure byregulation of the d point of the overhead fraction.

The various operations of our process may be illustrated by reference tothe drawing which shows one of the arrangements of equipmentv which aresuitable for practicing our invention.

The sour substantially butane-free gasoline enters by line I to column 2wherein the Cs hydrocarbons are taken overhead through line 3 tosweetening unit l and nce by line l to column I. In column l the isowtane is taken overhead through iine 1, while n-pentane is removed fromthe kettle throng line l to storage i. The isopentane passing thrughline 1 may pass directly tostorage through byepass line la, or it maypass through line I and "dehydrator Il to alkyl sulfide removal reagent(anhydrous cupric chloride) in vessel I2. From I2 the isopentane passesthrough'line I3 to storage I4.

The pentane-free bottoms fraction from column 2 passes through line Il'to sweetening unit Il, thence by line I1 to column Il. Column Il isoperated to take the desired portion of the pentane-free gasolineoverhead through line It. while the heavy bottoms pass through line 20to storage 2|. The overhead fraction passes through lines I 9 and Ita tostorage 2l. Alternately the stream may pass through lines I9 and 22 todehydrator Il, alkyl sulfide removal unit vIl and then by line 2l tostorage 26. In one adaptation of our process, column Il becomes theso-called de-oiling column for the production of oil-free pentane-freegasoline by the removal of high-boiling fractions from the pentane-freematerial. In other adaptations,l column I8 may be replaced by'a seriesof columns in which isohexane and isoheptane fractions are segregatedfrom the corresponding normal parafflns and higher boiling constituentsof the pentane-free gasoline. In such a sub-division of thefractionation operations necessary facilities are provided for theoperation of the separate columns and the isoparaflin fractions may'becombined or stored separately with intervening treatment for the removalof alkyl sulfldes if desired.

The sour gasoline charge to our process should be substantiallybutane-free to avoid inclusion of butane in the isopentane stock. Thiscondition is normally obtained since the butane fraction is ordinarilycarefully segregated for other uses. We have noted that the sequence ofoperations which is outlined above is necessary to obtain products ofthe lowest sulfur content and highest response to tetraethyllead. Thusthe separation of the Cs hydrocarbons prior to sweetening results in alower sulfur content for the pentanefree gasoline fraction than when thesweetening is performed on the total or butane-free gasoline stream., Ineffect our process results in the removal of sulfur from the Cs andhigher-boiling hydrocarbon fraction through inclusion of a 75 process isapparently Ibased on the distribution of mercaptans and disulndesthroughout the entire gasoline boiling range'in a manner not clearly-discernible from the boiling points of the pure sulfur compounds. Byourinitial fractionation,

0 a larger proportion of the mercaptan sulfur is included in the Csfraction than would be predicted from the mercaptan boiling pointslisted. Thus when the fractionation precedes sweetening, the mercaptans'are partly removed in the overhead pentane fraction and aresubsequently converted to disulfldes and concentrated in the lessvaluable n-pentane fraction by the fractionation which segregatesis'opentane. When the sweetening precedes the depentanizing step, the

o disulfldes formed are absent from the Cs fraction but are distributedthroughout the Cs and heavier fraction in the subsequent fractionationof this material. -This distribution results in a higher sulfur contentfor the intermediate boiling Ce and 25 C1 isoparafilns and/or for theoilfree pentanefree gasoline.

It will also be noted from the above description that in the separationof isopentane from n-pentane, the methyl sulfide present is concentrated0 almost entirely in the isopentane fraction although the boiling pointof methyl sulfide is slightly higher even than that of n-pentane.

By our initial fractionation, the methyl and ethyl mercaptans and a partof the isopropyl, t-

butyl and n-propyl mercaptans present in the sour gasoline are takenoverhead with the C hydrocarbons. This distillation euect is beneilcial'since the sweetening step converts these mercaptans to disulfides andthe boiling point 40 difference is then so great that the disulfides arecompletely concentrated in the n-pentane fraction. The inclusion ofmethyl and ethyl mercaptans in the Cs fraction is of additional benefitsince thedisulfides formed by sweetening have 5 boiling points of 244 F.and 307 F., respectively,

and thus are taken largely into a hydrocarbon fraction boiling as highas 300' F. When methyl and ethyl mercaptans are removed by our processfrom the Ca and heavier fraction prior to sweets0 ening there is acorresponding reduction in the sulfur content of the higher boilingstocks obtainable from the pentane-free gasoline.

The isopentane fraction produced by our process has a very low sulfurcontent which consists almost entirely of methyl sulfide. In some casesthe sulfur content is low enough to make further desulfurizationunnecessary. In other instances the methyl suide content may be largeenough to justify further treatment. We prefer to pass o the isopentanestream first through an efficient dehydrator-to remove water and thenthrough a bed of substantially anhydrous cupric halide reagent, usuallythe chloride, which effectively removes the methyl sulfide.

g5 The Ca and heavier fraction which has a reduced mercaptan contentfollowing the depentanizing operation is sweetened for conversion ofvthe remaining mercaptans to disulfldes. Since methyl mercaptan isabsent, the disulfldes formed 7o boil above about 300 F. and are thusalmost completely absent from intermediate fractions such as isohexanesand isoheptanes with end points below about 200 F., and are onlypartially included in fractions with end points up to about i 300 F. Thesulfur content of the lower-boiling stocks obtained by fractionation ofthe sweetened pentane-free gasoline of our process is thus reduced bythe distillation step. A treatment over the alkyl sulfide removalreagent as described for the isopentane eifectively removes the ethylsulfide also from the oil-free pentane-free gasoline or thelower-boiling isoparailln fractions thereof.

The following example will further illustrate the improved results to beobtained by our process. However, since many modifications of thedisclosed process are possible. no limitation is implied.

A sour butane-free natural gasoline had a total sulfur content of 0.045per cent. 'I'his gasoline. which was to serve as a source of isopentaneand of special high-octane blending stocks, was processed according toour invention, with the results recorded below. Other processing methodsthan those embodied in our invention were also evaluated. and thecomparative results are included to show the superiority of the presentinvention.

A portion ofthe sour to remove the Cn hydrocarbons. tion of sulfur wasas follows: f

gasoline was fractionated The distribu- Sample: Per cent sulfur lButane-free sour gasoline 0.045 Sour Cs fraction 0.036 Sour Cs andheavier pentane-free) fraction 0.055

Fractionation of the sour Cs. fraction without sweetening gave thefollowing results:

Sample: Per cent sulfur Sour isopentane 0.037 Sour n-pentane i-.. 0.037

WhenA the Cs fraction was sweetened prior to isopentane productionaccording to our invention. the resultant fractions had these sulfurcontents:

Per cent sulfur Sample:

Isopentane from sweetened Cs fraction 0.003 n-Pentane bottoms 0.061

'I'hus over 90- per cent of the sulfur occuring in the'Cs fraction isconcentrated in the n-pentane bottoms byl our process.y This removal ofsulfur from the isopentane is not possible when the sour Cs mixture isfractionated into iso and normal pentane prior to sweetening.

When the isopentane was dried and -passed over anhydrous cupric chloridereagent the sulfur content was reduced from 0.003 to 0.0008 per cent.

The sou-r pentane-free gasoline fraction (the bottom product) having asulfur content 'of 0.055 per cent was sweetened and then fractionated,taking varying volume percentages overhead to correspond to variousoil-free naphtha cuts. The sulfur content of the fractions was asfollows:

Sample: Per cent sulfur per cent overhead cut .0130 per cent overheadcut .0130 96.6 per cent overhead cut .0170v stock containing 0.023 percent produced, by our new Sample: Per cent sulfur Sour butane free gasoline. y .04:5 Sweet butane free gasoline .045 Cs fraction from above .002Cs and heavier fraction from above---" .092 Isopentane from Cs fraction..003 n-Pentane from Cs fraction.. .001

These results show that while the isopentane produced had a sulfurcontent comparable with that process, the sulfur content of thepentane-free fraction increased from 0.055 to 0.092, an increase ofalmost 65 per cent. The principal sulfur reduction was in the n-pentanefraction which is the least valuable blending stock, Subsequentfractionation of the Cs and heavier fraction with obiectionably highsulfur contents removable only with diihculty and at great expense.

The improved response to tetraethyl lead resulting from our new processis illustrated by the following comparison of theabove-describedpentane-free gasoline:

A. S. T. M. octane number Per f' cent sulfur Sample g1g; icc. zoe. 3cc.

c. and heavier onction mmroducod by new @te sans 0 n l!! le l 0 mitm...)

When the pentane-free fractions listed above were fractionated to removeabsorption oil and heavy ends, about 4 per cent of the material wasremoved as bottoms. The pentane-free, oil-free gasoline produced by ournew process had a sulfur content of 0.017 per cent, while that producedby the prior process had a sulfur content of 0.023 per cent. ..-Thus,content of the oil-free gasoline more than 35% below that obtained inthe conventional process.

-The pentane-free gasoline produced by our new process was fractionatedto produce an overhead f an end point of 195 F., and this specialnaphtha after treatment to remove alkyl fraction with onh'r 55 per centof isooctane in pound Reid vapor pressure oc- 'I'he correspondingpentane-free sulfur as stated per cent of isosulndes required preparinga 7 tane blend.

above required almost 59 volume octane to prepare the same blend.

The terms butane-free and pentane-free,

as employed herein, denote hydrocarbon mixtures containing not more thanfive (5) volume per cent of butane or pentane which have beensubstantially removed byv eilicient fractionating columns.

The sweetemng operations process may be any conventional sweeteningmethods wherein the mercaptans are substantially completely convertedtably the disuldes,

gave isohexanes and isoheptanes our process reduced the sulfur i assuch, since such modifications do not alter the fundamental features ofour process within the scope of the foreg-oing disclosure.

We claim:

. 1. The process of producing isopentane from a sour hydrocarbon oil inthe gasoline range which is substantially butane and hydrogen sulfidefree which comprises fractionating said oil to obtain as the overheadproduct a fraction comprising the pentanes containing mercaptans andmethyl sulfide, sweetening said pentane fraction, fractionating thesweetened pentane fraction to recover as tion comprising essentiallyisopentane and containing methyl sulfide but essentially free from otherforms of sulfur, and treating said isopentane fraction to remove saidmethyl sulfide and recover isopentane essentially free from sulfur.

2. The process of producing an isopentane fraction which comprisesfractionating sour gasoline which is substantially butaneand hydrogensulfide-free, to recover a fraction comprising essentially pentanes andcontaining lower mercaptans and methyl sulfide, sweetening said fractionto convert said mercaptans to disulfldes, fractionating said sweetenedfraction and recovering a normal pentane fraction containing said`dlsuldes and an isopentane fraction containing said methyl sulfide, andtreating said isopentane fraction to remove said methyl sulde therefromand form substantially pure isopentane.

3. The process of preparing alfraction of hydrocarbons consistingessentially of isopentane which comprises fractionating a sourhydrocarbon oil in the gasoline range which is substantially butane andhydrogen sulfide free into a pentane fraction and a heavier fraction,separately sweetening said fractions in such manner as to convertmercaptans therein to disuldes, and separately fractionating thesweetened fractions to recover from said pentane fraction a lightfraction of isopentane and a heavier n-pentane fraction in which thehigh boiling sulfur the overhead product a fraccompounds areconcentrated, and to recover from -y said first-named heavier fractionone or more light fractions comprising isohexane and isoheptane and aheavier fraction.

4. The process of preparing a fraction of hydrocarbons consistingessentially of isopentane which comprises fractionating a.v sourhydrocarbon oil in the gasoline range which is substantially butane andhydrogen sulilde free into a pentane fraction and a heavier fraction,separately sweetening said fractions in such manner as to convertmercaptans therein to disulfldes, separately fractionating the sweetenedfractions to recover from said pentane fraction a. light fraction ofisopentane and a heavier n-pentane fraction in which the high boilingsulfur compounds are concentrated, and to recover from said first-namedheavier fraction one or more light fractions comprising isohexane andisoheptane and a heavier fraction, and separately treating the lightfractions so produced to remove alkyl sulfldestherefrom.

5. The process of recovering high octane number gasoline blending stockof low sulfur content from sour hydrocarbon oil in the gasoline rangewhich is substantially butane and hydrogen sulfide free which comprisesfractionating said oil to remove overhead pentanes and a largeproportion of the sulfur compounds and form a bottom aarden product,sweetening the bottom product from said fractionation to convertremaining mercaptans therein to disulfldes, and fractionating thesweetened bottom product to recover at least one Vfraction ofsubstantially pentane-free and mersaid fractionation to convertremaining mercaptans therein to disulildes, fractionating. the sweetenedbottom product to recover at least one fraction of substantiallypentanefree and mercaptan-free material in the gasoline range, and

subjecting said pentane-free material 'to treat- .ment to remove alkylsulfides therefrom and form essentially sulfur-free material.

7. A process for the production of isopentane and pentane-free lightgasoline of lowered sulfur content from a 'sour butane and hydrogensulfide free hydrocarbon mixture containing same which comprisesfractionating said mixture to produce an overhead fraction consisting ofC5 hydrocarbons and a bottoms fraction consisting of substantiallypentane-free gasoline, treating said fractions in separate units toconvert the mercaptans contained therein to disulfide form,fractionating said C5 hydrocarbon fraction to produce an overheadfraction comprising isopentane and a bottoms fraction comprisingn-pentane, fractionating said substantially pentanefree gasoline toremove components boiling substantially above the gasoline rangetherefrom, and thereby obtaining an isopentane stock and a substantiallypentane-free gasoline stock of lowered sulfur content and improvedresponse to tetraethyl lead. Y

8. The process of claim 7 wherein the isopentane stock and thepentane-free gasoline stock are treated in substantially anhydrouscondition with a reagent comprising substantially anhydrous cupricchloride whereby alkyl sulfides are removed and said stocks of loweredsulfur con-` pentane-free gasoline stock subsequent to sweet- Iening isfractionated to produce an overhead fraction substantially lower boilingthan n-heptane and a bottoms fraction comprising n-heptane andhigher-boiling hydrocarbons, and wherein said overhead fraction and theisopentane stock are'treated in substantially anhydrous condition with areagent comprising substantially anhydrous cupric chloride wherebyxalkylsuldes are removed and said isopentane stock and said substantiallypentane-free n-heptane-free gasoine are obtained with lowered sulfurcontent and improved response to -tetraethyl lead.

10. A process for the production of isopentane and pentane-free lightgasoline of lowered sulfur content from a mixture comprising principallyhydrocarbons of 5 to 8 carbon atoms inclusive together with sulfurimpurities including mercaptans and alkyl suldes which comprisesfractionating said mixture to produce an overhead fraction consisting ofC5 hydrocarbons and a bottoms fraction consisting of substantiallypentanefree gasoline, treating said fractions in separate units toconvert the mercaptans contained therefrom a mixture comprisingprincipally hydrocarbons of 5 to 8 carbon atoms inclusive, together withsulfur impurities including mercaptans and alkyl suliides whichcomprises fractionating said mixture to produce an overhead fractionconsisting of C5 hydrocarbons and a bottoms fraction consisting ofsubstantially pentane-free gasoline, treating said fractions in separateunits to convert the mercaptans contained therein to disulfide form,fractionating said C5 hydrocarbon fraction to produce an overheadfraction comprising isopentane and a bottoms fraction comprising normalpentane, fractionating said substantially pentane-free gasoline toproduce an isohexanes fraction and an isoheptanes fraction and combiningsaid isohexanes and isoheptanes fractions to produce a high octaneisoparaiflnic gasoline of lowered sulfur content and improved responseto tetraethyl lead.

12. The process of claim 11 in which the high octane isoparanic gasolineis treated in substantially anhydrous condition with substantiallyanhydrous cupric chloride for the removal of alkyl sulfldes 13. Aprocess which comprises fractionating a sour hydrocarbon oil in thegasoline range which is substantially butane and hydrogen sulfide freeto obtain as an overhead product a fraction comprising the pentanes andas the bottom product a heavier substantially pentane-free fraction,sweetening said bottom product to con-4 vert mercaptans therein todisuldes, and fractionating said sweetened bottom product to separatelyrecover isohe'xane and isoheptane fractions of greatly reduced sulfurcontent and increased tetraethyl lead response.`

14. A process for the production of high octane isoparafnic gasolinefractions of lowered sulfur content from a butane-free predominantlysaturated gasoline having a boiling'range of from about '70 F. to about300 F.,and rcontaining sulfur impurities including mercaptans and alkylsuldes which comprises fractionating said gasoline -to produce fractionsconsisting essentially of hydrocarbons of the same number of carbonatoms, separately sweetening said fractionsr to f convert the mercaptansto disuldes, further fractionating the sweetened fractions to separate alower boiling isoparafiinic fraction from higher boiling normal parafiinfraction containing the disulfides, and recovering thereby isoparainicgasoline fractions of lowered sulfur content.

15. The process of claim 1 in which the isofparafiinic fractions aretreated in substantially anhydrous condition over a reagent comprisinganhydrous cupric chloride for the removal of alkyl suliides.

16. A process for the production of high octane isoparaffinic gasolinefractions of lowered sulfur content from a butane-free predominantlysaturated gasoline having a boiling range of from about '70 F. to about300 F. and containing sulfur impurities including mercaptans and alkylsuldes which comprises fractionating said gasoline to produce anoverhead fraction consisting of C`5 hydrocarbons and a bottoms fractionconsisting of substantially pentane-free gasoline, treating saidfractions in separate umts to convert the mercaptans contained thereinto disulfide form, fractionating said C5 fraction to produce an overheadfraction comprising isopentane and a bottoms fraction comprising normalpentane, fractionating said substantially pentane-free gasoline toproduce successively higher boiling fractions comprising respectivelyisohexanes, normal hexanes, isoheptanes, normal heptanes, isooctanes,normal octanes and isononanes with the highest boiling of saidsuccessive fractions having an end-point below about 300 F. and thetotal volume of said fractions not exceeding about 96 per cent of thetotal volume of pentane-free gasoline, and thereby separating andrecovering by means of said fractionations high octane isoparaiinicgasoline fractions from low octane normal parain gasoline fractions.

17. A process as in claim 2 wherein the isoparaflinic gasoline fractionsare treated for removal of alkyl suldes.

18. A process for the production of high octane number isoparaiilnicgasoline blending stocks of low sulfur content from sour hydrocarbon oilin the gasoline range which comprises fractionating said oil to removeoverhead pentanes and a large proportion of the sulfur compounds,sweetening the bottom product from said fractionation consisting oflhexanes and heavier hydrocarbons to convert remaining mercaptanstherein to disul- -fides, and fractionating the sweetened bottom

